Simulation-assisted metrology image alignment

ABSTRACT

A method for aligning a measured image of a pattern printed on a substrate with a design layout. The method includes: obtaining a design layout of a pattern to be printed on a substrate and a measured image of the pattern printed on the substrate; performing a simulation process to generate a plurality of simulated contours of the design layout for a plurality of process conditions of a patterning process; identifying a set of disfavored locations based on the simulated contours; and performing an image alignment process to align the measured image with a selected contour of the simulated contours using locations other than the set of disfavored locations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Application Ser. No. 63/116,385which was filed on 20 Nov. 2020, and which is incorporated herein in itsentirety by reference.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus for measuringpatterns formed by a patterning process on a substrate.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs) or other devices. In that instance, apatterning device, which is alternatively referred to as a mask or areticle, may be used to generate a pattern to be formed on an individuallayer of the IC. This pattern can be transferred onto a target portion(e.g., including part of, one, or several dies) on a substrate (e.g., asilicon wafer). Transfer of the pattern is typically via imaging onto alayer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a network ofadjacent target portions that are successively patterned. Knownlithographic apparatus include so-called steppers, in which each targetportion is irradiated by exposing an entire pattern onto the targetportion at one time, and so-called scanners, in which each targetportion is irradiated by scanning the pattern through a radiation beamin a given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti parallel to this direction. Itis also possible to transfer the pattern from the patterning device tothe substrate by imprinting the pattern onto the substrate.

In order to monitor one or more steps of a patterning process (i.e., aprocess of device manufacturing involving lithography, including, e.g.,resist-processing, etching, development, baking, etc.), the patternedsubstrate is inspected and one or more parameters of the patternedsubstrate are determined. The one or more parameters may include, forexample, edge placement errors (EPEs), which are distances between edgesof patterns formed on the substrate and corresponding edges of theintended design of the patterns. This measurement may be performed onpatterns of the product substrate itself and/or on a dedicated metrologytarget provided on the substrate. There are various techniques formaking measurements of the microscopic structures formed in a patterningprocess, including the use of a scanning electron microscope (SEM)and/or various specialized tools.

SUMMARY

In an aspect, there is provided a non-transitory computer-readablemedium having instructions that, when executed by a computer, cause thecomputer to execute a method for aligning a measured image of a patternprinted on a substrate with a design layout. The method includes:obtaining a design layout of a pattern to be printed on a substrate anda measured image of the pattern printed on the substrate; performing asimulation process to generate simulated contours of the design layoutfor a plurality of process conditions of a patterning process;identifying a set of disfavored locations based on the simulatedcontours; and performing an image alignment process to align themeasured image with a selected contour of the simulated contours usinglocations other than the set of disfavored locations

In an aspect, there is provided a non-transitory computer-readablemedium having instructions that, when executed by a computer, cause thecomputer to execute a method for aligning a measured image of a patternprinted on a substrate with a design layout. The method includes:obtaining a design layout of a pattern to be printed on a substrate anda measured image of the pattern printed on the substrate; performing asimulation process to generate a plurality of simulated results of thedesign layout for a plurality of process conditions of a patterningprocess; identifying a set of disfavored locations based on thesimulated results; and performing an image alignment process between themeasured image and the design layout by aligning the measured image witha selected result of the simulated results using locations other thanthe set of disfavored locations.

In an aspect, there is provided a non-transitory computer-readablemedium having instructions that, when executed by a computer, cause thecomputer to execute a method for aligning a measured image of a patternprinted on a substrate with a design layout. The method includes:obtaining a design layout of a pattern to be printed on a substrate anda measured image of the pattern printed on the substrate; performing asimulation process to generate simulated contours of the design layoutfor a plurality of process conditions of a patterning process;identifying a set of disfavored locations based on the simulatedcontours; performing a simulation process to generate a predictedmeasured image from a selected contour of the simulated contours; andperforming an image alignment process to align the measured image withthe predicted measured image using locations other than the set ofdisfavored locations.

In an aspect, there is provided a method for aligning a measured imageof a pattern printed on a substrate with a design layout. The methodincludes: obtaining a design layout of a pattern to be printed on asubstrate and a measured image of the pattern printed on the substrate;performing a simulation process to generate a plurality of simulatedcontours of the design layout for a plurality of process conditions of apatterning process; identifying a set of disfavored locations based onthe simulated contours; and performing an image alignment process toalign the measured image with a selected contour of the simulatedcontours using locations other than the set of disfavored locations.

In an aspect, there is provided an apparatus for aligning a measuredimage of a pattern printed on a substrate with a design layout. Theapparatus includes: a memory storing a set of instructions; and at leastone processor configured to execute the set of instructions to cause theapparatus to perform a method of: obtaining a design layout of a patternto be printed on a substrate and a measured image of the pattern printedon the substrate; performing a simulation process to generate aplurality of simulated contours of the design layout for a plurality ofprocess conditions of a patterning process; identifying a set ofdisfavored locations based on the simulated contours; and performing animage alignment process to align the measured image with a selectedcontour of the simulated contours using locations other than the set ofdisfavored locations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an embodiment of a lithographic apparatus,in accordance with one or more embodiments.

FIG. 2 schematically depicts an embodiment of a lithographic cell orcluster, in accordance with one or more embodiments.

FIG. 3 schematically shows a process of aligning an image to a portionof a design layout, in accordance with one or more embodiments.

FIG. 4 schematically shows a simulation flow chart, in accordance withone or more embodiments.

FIG. 5 shows a block diagram of a system for facilitating asimulation-assisted alignment of a metrology image with a design layout,in accordance with one or more embodiments.

FIG. 6 shows an example of a post-resolution enhancement techniquedesign layout, in accordance with one or more embodiments.

FIG. 7 shows an example of simulated contours corresponding to variousprocess conditions, in accordance with one or more embodiments.

FIG. 8 shows an example of favored locations and disfavored locations ofthe design layout, in accordance with one or more embodiments.

FIG. 9 shows a set of favored locations on a nominal contour of a designlayout and on a metrology image for performing the alignment, inaccordance with one or more embodiments.

FIG. 10 shows an example of resizing a simulated contour for alignmentwith a metrology image, in accordance with one or more embodiments.

FIG. 11 shows a block diagram of another system for facilitating asimulation-assisted alignment of a metrology image with a design layout,in accordance with one or more embodiments.

FIG. 12 is a flow diagram of a method of aligning a portion of a designlayout and a metrology image obtained from a patterned substrate, inaccordance with one or more embodiments.

FIG. 13 is a block diagram of an example computer system, in accordancewith one or more embodiments.

DETAILED DESCRIPTION

In order to monitor one or more steps of a patterning process (i.e., aprocess of device manufacturing involving lithography, including, e.g.,resist-processing, etching, development, baking, etc. for transferring adesign layout (e.g., target pattern) onto a substrate), a patternedsubstrate is inspected and one or more parameters of the patternedsubstrate are determined. The one or more parameters may include, forexample, edge placement errors (EPEs), which are distances between edgesof patterns formed on the substrate and corresponding edges of theintended design of the patterns. Based on these parameters, one or moreaspects of the design layout, the patterning process, or thelithographic apparatus may be adjusted to minimize a defect andtherefore, improve the overall yield of the patterning process.

Some inspection methods for determining one or more parameters of apatterned substrate include a simulation-assisted alignment method inwhich a measured image (also referred to as a “metrology image” and maybe an image of a pattern printed on a substrate, such as a scanningelectron microscope (SEM) image) is aligned with a design layout (e.g.,target pattern to be printed on the substrate) to determine the one ormore parameters. In the simulation-assisted alignment method, themetrology image is aligned with a simulated contour of the design layoutto determine the one or more parameters. However, these methods havesome drawbacks. For example, while these methods avoid performingalignment at reference locations that may be prone to large EPE, they donot consider factors other than EPE in choosing or not choosing thereference locations for performing the alignment causing the alignmentto be sub-optimal, which may result in the values of the one or moreparameters being inaccurate. In another example, these methods do notconsider process variations of the patterning process (e.g., lens effectof the lithographic apparatus, resist effect of a resist on thesubstrate, or other such variations) in generating the simulatedcontours, which may result in sub-optimal alignments. In anotherexample, these methods do not consider resizing the simulated contour tomatch the contour from the metrology image, which may result insub-optimal alignment. In another example, these methods do notfacilitate generating a simulated metrology image and performing analignment between the simulated metrology image and the metrology image.These and other drawbacks exist.

Embodiments of the present disclosure facilitate alignment of ametrology image and a simulated contour by identifying a set of“favored” locations associated with a design layout to be used forperforming the alignment with the metrology image and a set of“disfavored” locations to be avoided from being used for performing thealignment. In some embodiments, the alignment may be performedsubstantially concurrent with metrology image capturing on an inspectiontool. The embodiments may perform the alignment of the design layoutwith the metrology image at locations other than the set of disfavoredlocations. In some embodiments, the favored or disfavored locations areidentified based one or more criteria, such as EPE, process variationrange, symmetricity, or other such aspects associated with a location onthe design layout. For example, the embodiments may identify thoselocations as disfavored locations at which (a) a number of simulatedcontours of the design layout have a process variation range exceeding afirst threshold, (b) the simulated contours have an EPE exceeding asecond threshold, (c) the simulated contours are asymmetric, or (d) oneor more simulated contours are broken. In some embodiments, a user maycustomize the criteria for selecting the disfavored locations. Theembodiments may also facilitate in resizing a simulated contour of thedesign layout at one or more favored locations to match the contour fromthe metrology image to further improve an accuracy of the alignment. Theembodiments may also facilitate generating a simulated metrology imagefrom the simulated contour and performing an alignment between thesimulated metrology image and the metrology image.

Before describing embodiments in detail, it is instructive to present anexample environment in which embodiments may be implemented.

FIG. 1 schematically depicts a lithographic apparatus LA, in accordancewith one or more embodiments. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation, DUV radiation or EUV        radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PL configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W, the projection        system supported on a reference frame (RF).

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any

device that can be used to impart a radiation beam with a pattern in itscross-section such as to create a pattern in a target portion of thesubstrate. It should be noted that the pattern imparted to the radiationbeam may not exactly correspond to the desired pattern in the targetportion of the substrate, for example if the pattern includesphase-shifting features or so-called assist features. Generally, thepattern imparted to the radiation beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam, which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore tables (e.g., two or more substrate tables WTa, WTb, two or morepatterning device tables, a substrate table WTa and a table WTb belowthe projection system without a substrate that is dedicated to, forexample, facilitating measurement, and/or cleaning, etc.). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure. For example, alignmentmeasurements using an alignment sensor AS and/or level (height, tilt,etc.) measurements using a level sensor LS may be made.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the patterning device and the projection system Immersiontechniques are well known in the art for increasing the numericalaperture of projection systems. The term “immersion” as used herein doesnot mean that a structure, such as a substrate, must be submerged inliquid, but rather only means that liquid is located between theprojection system and the substrate during exposure.

Referring to FIG. 1 , the illuminator IL receives a radiation beam froma radiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD configured to adjust theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PL,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder, 2-D encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g. so as toposition different target portions C in the path of the radiation beamB. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in FIG. 1 ) can be used to accuratelyposition the patterning device MA with respect to the path of theradiation beam B, e.g. after mechanical retrieval from a mask library,or during a scan. In general, movement of the support structure MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table

WT may be realized using a long-stroke module and a short-stroke module,which form part of the second positioner PW. In the case of a stepper(as opposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

-   -   1. In step mode, the support structure MT and the substrate        table WT are kept essentially stationary, while an entire        pattern imparted to the radiation beam is projected onto a        target portion C at one time (i.e. a single static exposure).        The substrate table WT is then shifted in the X and/or Y        direction so that a different target portion C can be exposed.        In step mode, the maximum size of the exposure field limits the        size of the target portion C imaged in a single static exposure.    -   2. In scan mode, the support structure MT and the substrate        table WT are scanned synchronously while a pattern imparted to        the radiation beam is projected onto a target portion C (i.e. a        single dynamic exposure). The velocity and direction of the        substrate table WT relative to the support structure MT may be        determined by the (de-)magnification and image reversal        characteristics of the projection system PL. In scan mode, the        maximum size of the exposure field limits the width (in the        non-scanning direction) of the target portion in a single        dynamic exposure, whereas the length of the scanning motion        determines the height (in the scanning direction) of the target        portion.    -   3. In another mode, the support structure MT is kept essentially        stationary holding a programmable patterning device, and the        substrate table WT is moved or scanned while a pattern imparted        to the radiation beam is projected onto a target portion C. In        this mode, generally a pulsed radiation source is employed and        the programmable patterning device is updated as required after        each movement of the substrate table WT or in between successive        radiation pulses during a scan. This mode of operation can be        readily applied to maskless lithography that utilizes        programmable patterning device, such as a programmable mirror        array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

As shown in FIG. 2 , the lithographic apparatus LA may form part of alithographic cell LC, also sometimes referred to a lithocell or cluster,which also includes apparatuses to perform pre- and post-exposureprocesses on a substrate. Conventionally these include one or more spincoaters SC to deposit one or more resist layers, one or more developersDE to develop exposed resist, one or more chill plates CH and/or one ormore bake plates BK. A substrate handler, or robot, RO picks up one ormore substrates from input/output port I/O1, I/O2, moves them betweenthe different process apparatuses and delivers them to the loading bayLB of the lithographic apparatus. These apparatuses, which are oftencollectively referred to as the track, are under the control of a trackcontrol unit TCU which is itself controlled by the supervisory controlsystem SCS, which also controls the lithographic apparatus vialithography control unit LACU. Thus, the different apparatuses can beoperated to maximize throughput and processing efficiency.

In order that a substrate that is patterned by the lithographicapparatus is done so correctly and consistently, it is desirable toinspect a patterned substrate to measure one or more properties such asEPEs, line thickness, critical dimension (CD), etc. Accordingly, amanufacturing facility in which the lithocell LC is located alsotypically includes a metrology system MET which receives some or all ofthe substrates W that have been processed in the lithocell. Themetrology system MET may be part of the lithocell LC, for example it maybe part of the lithographic apparatus LA.

Metrology results may be provided directly or indirectly to thesupervisory control system SCS. If an error is detected, an adjustmentmay be made to patterning of a subsequent substrate (especially if theinspection can be done soon and fast enough that one or more othersubstrates of the batch are still to be patterned) and/or to subsequentpatterning of the patterned substrate. Also, an already patternedsubstrate may be stripped and reworked to improve yield, or discarded,thereby avoiding performing further processing on a substrate known tobe faulty. In a case where only some target portions of a substrate arefaulty, further patterning may be performed only on those targetportions which are good.

Within a metrology system MET, an inspection apparatus is used todetermine one or more properties of the substrate, and in particular,how one or more properties of different substrates vary or differentlayers of the same substrate vary from layer to layer. The inspectionapparatus may be integrated into the lithographic apparatus LA or thelithocell LC or may be a stand-alone device. To enable rapidmeasurement, it is desirable that the inspection apparatus measures oneor more properties in the patterned resist layer immediately after thepatterning. However, for example, a latent image in the resist has a lowcontrast — there is only a very small difference in refractive indexbetween the parts of the resist which have been exposed to radiation andthose which have not—and not all inspection apparatus have sufficientsensitivity to make useful measurements of the latent image. Thereforemeasurements may be taken after the post-exposure bake step (PEB) whichis customarily the first step carried out on an exposed substrate andincreases the contrast between exposed and unexposed parts of theresist. At this stage, the image in the resist may be referred to assemi-latent. It is also possible to make measurements of the developedresist image—at which point either the exposed or unexposed parts of theresist have been removed—or after a pattern transfer step such asetching. The latter possibility limits the possibilities for rework of afaulty substrate but may still provide useful information.

The inspection of a substrate patterned in a patterning process mayinvolve capturing images (e.g., scanning electron microscopy images) ofthe substrate. Some parameters of the patterned substrate may beextracted from the images alone but other parameters may requirecomparison with other data, such as the design layout of the patternsformed on the substrate.

Comparing the design layout to an image is not always straightforward.The image may have to be aligned to the design layout before thecomparison. Errors in the alignment may lead to errors in the parametersof the patterned substrate measured by the metrology system. FIG. 3schematically shows a process of aligning an image to a portion of adesign layout,

in accordance with one or more embodiments. An image 2010 is obtained,for example, from an image capture device, e.g., an inspection apparatusof the metrology system. The image 2010 may be a metrology image ofpatterns formed on a substrate from the portion of the design layoutusing a patterning process. The image 2010 may be a pixelated image suchas a SEM image Contours 2020 may be identified from the image 2010,using a suitable edge detection algorithm. The contours 2020 representthe edges of the patterns on the substrate. The contours 2020 and theportion of the design layout 2030 are used to determine a mappingbetween the portion of the design layout 2030 and the image 2010 foraligning the portion of the design layout 2030 and the image 2010. Theword “mapping” here may represent relative translation, relativerotation, relative scaling, relative skewing or other relativedeformation, which may be applied to the image 2010 before the image2010 and the portion of the design layout 2030 are aligned. There may bemultiple mappings that are all reasonable, which result in multipledifferent alignments (e.g., 2040A and 2040B) of the portion of thedesign layout 2030 and the image 2010. In the different alignments, theparameters of the patterned substrate measured by the metrology systemmay have different values.

There may be multiple ways to use the contours 2020 and the portion ofthe design layout 2030 to determine the mapping between them. Forexample, a cost function may be defined to characterize deviations ofcorresponding mapping references (e.g., edges, corners) in the contours2020 and in the portion of the design layout 2030. The term “mappingreference” as used herein means a portion of a design layout or of animage, based on which the mapping between the design layout and theimage is determined. In an example, the cost function may be expressedas

CF(m)=Σ_(p=1) ^(P) w _(p) f _(p) ²(m)  (Eq. 1)

wherein m is the mapping and f_(p)(m) can be a function of the mappingm. For example, f_(p)(m) can be a deviation between a mapping referencein the contours 2020 and a corresponding mapping reference in theportion of the design layout 2030. The deviation here may includerelative translation, relative rotation, relative scaling, relativeskewing or other relative deformation. w_(p) is a weight constantassociated with f_(p)(m). EPE is one example of f_(p)(m). Differentf_(p)(m) may have equal weight w_(p), especially when there is no reasonto favor some f_(p)(m) relative to others. Of course, CF(m) is notlimited to the form in Eq. 1. CF(m) can be in any other suitable form.The mapping m may be one that minimizes or maximizes the cost functionCF(m).

Not all of the mapping references of the design layout may be producedon a substrate with equal accuracy by a patterning process. Some of themapping references of the design layout may have large deviations fromthe corresponding mapping references of the patterns produced on thesubstrate. The deviations may have multiple origins. One origin can be aresolution enhance technique (RET). In order to accurately producepatterns with dimensions smaller than the classical resolution limit ofa lithographic projection apparatus, sophisticated fine-tuning steps maybe applied to the lithographic projection apparatus and/or the designlayout. RETs may include, for example, but not limited to, optimizationof NA and optical coherence settings, customized illumination schemes,use of assist features, use of phase shifting patterning devices,optical proximity correction (OPC) in the design layout, etc. RETs maynot be perfect and may contribute to the deviations.

Another origin can be inaccuracy of the patterning device (sometimescalled “mask errors”). After the design layout is modified by a RET, itcan be formed on or by a patterning device. This process may haveerrors. Namely, a pattern as a result of a RET may not be accuratelyformed on or by the patterning device. For example, a pattern formed onor by the patterning device may have a deformation such as a translationof edges of the pattern, a translation of the pattern, a rotation ofedges of the pattern, scaling of the pattern, and/or skewing of thepattern, relative to the design layout or the post-RET layout.

Yet another origin can be the patterning process, including alithographic projection apparatus used therein. The patterning processmay have various errors. Examples of errors may include that the resistused on the substrate has a development rate higher than normal, that aradiation source output is lower than normal, that a component in theprojection optics is deformed due to heating, and/or a stochastic effectof photon shot noise.

At least a portion of a deviation between a mapping reference of thedesign layout and the corresponding mapping reference of the patternproduced on the substrate may be determined based on simulation andcharacteristics of the patterning process (including the lithographicapparatus) and the design layout. The simulation may provide informationthat can be used to determine the mapping between a metrology image(e.g., image 2010) and the design layout (e.g., the portion 2030).

FIG. 4 schematically shows a simulation flow chart, in accordance withone or more embodiments. A source model 31 represents one or moreoptical characteristics (including radiation intensity distributionand/or phase distribution) of illumination. A projection optics model 32represents one or more optical characteristics (including changes to theradiation intensity distribution and/or the phase distribution caused bythe projection optics) of the projection optics. A patterning devicemodel 35 represents one or more optical characteristics of thepatterning device (including changes to the radiation intensitydistribution and/or the phase distribution caused by a given designlayout represented on the patterning device). An aerial image 36 can besimulated from the source model 31, the projection optics model 32 andthe patterning device model 35. A resist image 38 can be simulated fromthe aerial image 36 using a resist model 37. The resist model 37represents physical and chemical properties of the resist (e.g.,behavior of the resist in exposure, post exposure bake and development).An etch image 40 can be simulated from the resist image 38 using anetching model 39. The etching model 39 represents characteristics of theetching process of the substrate.

More specifically, the source model 31 can represent one or more opticalcharacteristics of the illumination including, but not limited to, anumerical aperture setting, an illumination sigma (σ) setting and/or aparticular illumination shape (e.g. off-axis illumination such asannular, quadrupole, dipole, etc.). The projection optics model 32 canrepresent one or more optical characteristics of the projection optics,including aberration, distortion, one or more refractive indices, one ormore physical sizes, one or more physical dimensions, etc. Thepatterning device model 35 can represent one or more physical propertiesof a physical patterning device, as described, for example, in U.S. Pat.No. 7,587,704, which is incorporated by reference in its entirety. Theetching model 39 can represent one or more characteristics of theetching process such as gas composition, (microwave) power, duration,one or more materials of the substrate, etc.

The source model 31, the projection optics model 32, the patterningdevice model 35, and the etching model 39 may model contributions of thepatterning process to deviations of the aerial, resist or etched imagefrom the design layout. The patterning device model 35 may model thecontribution of the RETs and inaccuracy of the patterning device todeviations of the aerial, resist or etched image from the design layout.The various models may be calibrated at least partially fromexperimental data.

The simulation may or may not simulate an aerial, resist or etchedimage. In the latter case, it can generate one or more variouscharacteristics thereof. For example, the simulation may simulate one ormore geometrical characteristics (position, orientation, or size) of amapping reference in the aerial, resist or etched image.

The simulation can provide information about the deviation of one ormore mapping references of a pattern produced on the substrate relativeto the design layout. The one or more mapping references that have largedeviations from the design layout as predicted by the simulation maynegative impact the alignment of a metrology image (e.g., image 2010)and the design layout (e.g., the portion 2030) and are given less orzero weight according to embodiments of the present disclosure.

FIG. 5 shows a block diagram of a system 500 for facilitating asimulation-assisted alignment of a metrology image with a design layout,in accordance with one or more embodiments. A file component 501 obtainsa design layout 502 (or a portion thereof) and a measured image 504(also referred to as “metrology image 504”). The design layout 502 maybe representative of a target pattern to be printed on a substrate, andthe metrology image 504 may be an image of a pattern formed on thesubstrate from the portion of the design layout 502. The metrology image504 may be a SEM image, which may be obtained from an inspectionapparatus, such as the SEM, of the metrology system of FIG. 2 . In someembodiments, the design layout 502 is obtained from Graphic DatabaseSystems (GDS) polygons associated with the target pattern. The GDSpolygons can be in one or more formats selected from GDS stream format(GDSII) and Open Artwork System Interchange Standard (OASIS). In someembodiments, the design layout 502 is similar to the design layout 2030,and the metrology image 504 may be similar to the image 2010 of FIG. 3 ,respectively.

After the design layout 502 is obtained, a RET (e.g., OPC) may beperformed on the design layout 502, which changes the design layout 502to a post-RET layout, such as the post-RET layout 605 of FIG. 6 . FIG. 6shows an example of a post-RET design layout 605, in accordance with oneor more embodiments. In some embodiments, RET may alter some of thepatterns and add assist features to the design layout 502.

A contour simulator 506 may produce a simulated contour, such as thesimulated contour

705 of FIG. 7 , based on the design layout 502 or the post-RET layout605. FIG. 7 shows an example of simulated contours 715 corresponding tovarious process conditions, in accordance with one or more embodiments.In some embodiments, the contour simulator 506 may generate a simulatedcontour 705 using the simulation process described at least withreference to FIG. 4 . In some embodiments, a number of processconditions, such as a lens effect (e.g., dose, focus, lens aberration,or other conditions) of the lithographic apparatus, a resist effect of aresist on the substrate, or other such process conditions, may have aneffect on the formation of a pattern on the substrate. Accordingly, thecontour simulator 506 may generate a number of simulated contours 715for a given target pattern, each corresponding to a different processcondition.

In some embodiments, the metrology image 504 may be aligned with thedesign layout 502 by aligning the metrology image 504 (or contoursgenerated from the metrology image 504) with a selected contour 520 ofthe design layout 502. In some embodiments, the selected contour 520 isone of the simulated contours 715 of the design layout 502 thatcorresponds to a specific process condition, e.g., a nominal processcondition.

A contour analyzer 508 may analyze the simulated contours 715 toidentify a set of “favored” locations 510 and a set of “disfavored”locations 512 for use in an alignment process. In some embodiments, theset of favored locations 510 may be portions of the selected contour 520(e.g., also referred to as mapping references as described at least withreference to FIG. 3 ) that, when used for aligning the metrology image504 with the nominal contour 520, aligns the metrology image 504 withthe design layout 502 with a greater accuracy than when aligned usingother locations of the nominal contour 520. For example, the costfunction, CF(m), may be optimized (e g , minimized or maximized) whenthe metrology image 504 and the nominal contour 520 are aligned usingthe set of favored locations 510 of the nominal contour 520 and thecorresponding locations of a contour of the metrology image 504. In someembodiments, the set of “disfavored” locations 512 may be portions ofthe nominal contour 520 to be avoided for performing the alignment, forexample, as they tend to impair accuracy in the alignment. For example,the deviations between the set of disfavored locations 512 on thenominal contour 520 and the corresponding locations of a contour of themetrology image 504 are very large and therefore, cannot lead to anoptimal cost function, CF(m).

In some embodiments, the contour analyzer 508 may identify the favoredor disfavored locations based on one or more criteria, such as EPE,process variation range, symmetricity, or other such aspects associatedwith a location on the design layout 502. For example, the contouranalyzer 508 may identify those locations as disfavored locations 512 atwhich (a) the simulated contours 715 of the design layout 502 have aprocess variation range satisfying (e.g., exceeding) a first processvariation threshold, (b) the simulated contours 715 have an EPEsatisfying (e.g., exceeding) a first EPE threshold, (c) the simulatedcontours 715 are asymmetric, or (d) one or more simulated contours 715are broken. FIG. 8 shows an example of favored locations and disfavoredlocations of the design layout, in accordance with one or moreembodiments. The locations, such as locations 810-830, enclosed in ovalboxes may be identified as the set of disfavored locations 512. Forexample, the process variation range (e.g., a variation between a numberof simulated contours 715 or a degree of non-overlap between thecontours 715) at the locations 810 and 830 is above a first processvariation threshold, or an EPE is above a first EPE threshold, andtherefore, the locations 810 and 830 may be identified as disfavoredlocations. In another example, the location 815 may be identified asdisfavored location as one or more simulated contours are broken. Inanother example, location 825 may be identified as a disfavored locationas the contours do not extend symmetrically on both sides of a referencepoint 820 (e.g., reference point 820 may be at half of the width betweenthe outermost contours in the location 825).

In some embodiments, the contour analyzer 508 may identify thoselocations as favored locations 510 at which (a) the simulated contours715 of the design layout 502 have a process variation range satisfying(e.g., below) a second process variation threshold, (b) the simulatedcontours 715 have an EPE satisfying (e.g., below) a second EPEthreshold, (c) the simulated contours 715 are symmetric, or other suchcriterion. In some embodiments, the contour analyzer 508 may identifythe locations, such as locations 805, 850 and 855, enclosed inrectangular boxes as the set of favored locations 510. For example, theprocess variation range at the locations 805, 850 and 855 is below asecond process variation threshold, or an EPE is below a second EPEthreshold, and therefore, the locations 805, 850 and 855 may beidentified as favored locations.

In some embodiments, a user may customize the criteria for selecting thefavored locations 510 or the disfavored locations 512. For example, theuser may define a criterion that even if the process variation is notbelow a second process variation threshold, but the contours extendsymmetrically around a reference point, then the reference point may beidentified as a favored point. Accordingly, the location 830 which wouldhave been identified as a disfavored location may be identified as afavored location since the contours extend symmetrically on both sidesof a reference point 835.

A first aligner 514 obtains information regarding the nominal contour520 and a number of locations (e.g., the set of favored locations 510and the set of disfavored locations 512) from the contour analyzer 508that may be used in aligning the metrology image 504 with the designlayout 502. After obtaining the information, the first aligner 514includes the set of favored locations 510 and excludes the set ofdisfavored locations 512 from a list of locations that may be used forperforming the alignment. The first aligner 514 may identify the set offavored locations 510 on the nominal contour 520 and the metrology image504 as shown in FIG. 9 . FIG. 9 shows a set of favored locations on anominal contour of a design layout and on a metrology image forperforming the alignment, in accordance with one or more embodiments.The first aligner 514 identifies the set of favored locations 510, suchas locations 905 a, 950 a and 955 a on the nominal contour 520 and thecorresponding locations 905 b, 950 b and 955 b on the metrology image504. The favored locations 905 a, 950 a and 955 a and 905 b, 950 b and955 b correspond to the favored locations 805, 850 and 855 of FIG. 8 .After identifying the favored locations on the nominal contour 520 andthe metrology image 504, the first aligner 514 may perform the alignmentprocess, which aligns the favored locations 905 b, 950 b and 955 b ofthe metrology image 504 with the favored locations 905 a, 950 a and 955a of the nominal contour 520, thereby aligning the metrology image 504with the design layout 502.

In some embodiments, a further alignment, referred to as “fine”alignment, may be performed to better align the metrology image 504 withthe nominal contour 520. A contour resizer 524 may adjust the nominalcontour 520 at one or more favored locations to match with acorresponding contour of the metrology image 504. FIG. 10 shows anexample of resizing a simulated contour for alignment with a metrologyimage, in accordance with one or more embodiments. For example, contourresizer 524 may resize the nominal contour 520 at the favored locations905 a and 950 a to reduce (e g , minimize) a deviation between thenominal contour 520 and the contour of the metrology image 504 at thefavored locations 905 a and 950 a so that the nominal contour 520matches, or better aligns with, the corresponding favored locations ofthe contour of the metrology image 504. The contour resizer 524 mayanalyze the metrology image 504 to obtain one or more measurementsassociated with the contour at the favored locations 905 b and 950 b anddirections 1005 a and 1005 b in which the nominal contour 520 is to beadjusted. The contour resizer 524 may resize the nominal contour 520accordingly to generate an adjusted nominal contour 530.

A second aligner 528 may perform the alignment process (e.g., in a waysimilar to the first aligner 514) to align the metrology image 504 withthe adjusted nominal contour 530, thereby aligning the metrology image504 with the design layout 502 with a greater accuracy than the firstaligner 514. In some embodiments, the fine alignment may be an optionalalignment process. For example, after the metrology image 504 is alignedwith the design layout 502 using the first aligner 514, it is determinedwhether an alignment specification is satisfied (e.g., a cost functionis optimized). If the alignment specification is satisfied, the secondalignment may not be performed. If the alignment specification is notsatisfied, the metrology image 504 is input to the second aligner 528,which performs the second alignment such that the alignmentspecification is satisfied (e.g., a cost function is minimized). In oneexample, the cost function may be an EPE, which may be calculated basedon the distances between points on the adjusted nominal contour 530 andthe contour of the metrology image 504.

After the metrology image 504 is aligned with the design layout 502(e.g., using the first aligner 514 or the second aligner 528), one ormore parameters (e.g., EPEs) of the patterned substrate are determinedfrom the metrology image 504 aligned with the design layout 502. Thedesign layout, the RETs, the patterning device, or the patterningprocess may be adjusted based on the one or more parameters so that adefect caused during the patterning process may be minimized

FIG. 11 shows a block diagram of a system 100 for facilitating asimulation-assisted 35 alignment of a metrology image with a designlayout, in accordance with one or more embodiments. In some embodiments,the system 1100 is similar to the system 500 of FIG. 5 except for somedifferences, which are described below. The description offunctionalities that are similar to the system 500 are omitted here forthe sake of brevity. After the nominal contour 520, the set of favoredlocations 510 and the set of disfavored locations 512 are determined asdescribed at least with reference to FIG. 5 , an image generator 1105may generate a predicted or simulated metrology image 1110 based on thenominal contour 520. The first aligner 514 may then align the metrologyimage 504 with the design layout 502 by aligning the metrology image 504with the simulated metrology image 1110. Similarly, the contour resizer524 may adjust the simulated metrology image 1110 (e.g., resize contourof the simulated metrology image 1110 at one or more favored locations)for matching the contour of the metrology image 504. The adjustedsimulated metrology image 1115 may then be input to the second aligner528 for aligning with the metrology image 504.

FIG. 12 is a flow diagram of a method 1200 of aligning a portion of adesign layout and a metrology image obtained from a patterned substrate,in accordance with one or more embodiments. In some embodiments, themethod 1200 may be implemented using the system 500 of FIG. 5 or system1100 of FIG. 11 . In process P1201, a design layout 502 (or post-RETlayout 605), a metrology image 504 and process conditions 1205 which arecharacteristic of the design layout 502, a patterning process, or thepatterning device used in producing the patterned substrate areobtained.

In process P1202, a simulation process is performed to produce an image1210 (e.g., an aerial, resist or etched image), which includes a numberof simulated contours of the design layout 502, such as simulatedcontours 715 of FIG. 7 . In some embodiments, each simulated contour maycorrespond to a different process condition 1205. In some embodiments,the simulation process (or even method 1200) may be performedsubstantially in real-time (e.g., upon determining the locations of thepatterned substrate to be inspected by an inspection apparatus), and inconcurrence with obtaining the metrology image 504 from the inspectionapparatus.

In process P1203, a number of locations 1215 associated with the designlayout 502 may be identified for performing an alignment with themetrology image. In some embodiments, the identified locations 1215 mayinclude a set of “favored” locations 510 and a set of “disfavored”locations 512. In some embodiments, the set of favored locations 510 maybe portions of the nominal contour 520 (e.g., one of the simulatedcontours 715) that, when used for aligning the metrology image 504,aligns the metrology image 504 with the design layout 502 with a greateraccuracy than when aligned using other locations of the nominal contour520. In some embodiments, the set of “disfavored” locations 512 may beportions of the nominal contour 520 to be avoided from being used forperforming the alignment as they provide less or no accuracy in aligningthe metrology image 504 with the design layout 502.

In process P1204, an alignment process is performed to align themetrology image 504 with the design layout 502. In some embodiments, themetrology image 504 may be aligned with the design layout 502 byaligning the metrology image 504 (or contours generated from themetrology image 504) with the nominal contour 520 of the design layout502. The alignment process may align the metrology image 504 with thenominal contour 520 using locations other than the set of disfavoredlocations 512. For example, the alignment process may align themetrology image 504 with the nominal contour 520 using the set offavored locations 510. In some embodiments, the alignment process mayperform a second alignment, e.g., to better align the metrology image504 with the design layout 502. For example, in the second alignment,the nominal contour 520 may be adjusted (e.g., resized) at one or moreof the favored locations to match a corresponding contour of themetrology image 504, and the metrology image 504 may then be alignedwith the adjusted nominal contour 530 to obtain an alignment with agreater accuracy than the first alignment. In some embodiments, asdescribed at least with reference to FIG. 11 , the alignment process mayalign the metrology image 504 with the design layout using a simulatedmetrology image. For example, the alignment process may align themetrology image 504 with the design layout 502 by aligning the metrologyimage 504 with the simulated metrology image 1110. The contour resizer524 may adjust the simulated metrology image 1110 (e.g., resize contourof the simulated metrology image 1110 at one or more favored locations)for matching the contour of the metrology image 504. The adjustedsimulated metrology image 1115 may then be input to the second alignmentprocess for performing a fine alignment with the metrology image 504.

After performing the alignment process, one or more parameters (e.g.,EPEs) of the patterned substrate are determined from the metrology image504 aligned with the design layout 502. The design layout, the RETs, thepatterning device, and/or the patterning process may be adjusted basedon the parameters.

FIG. 13 is a block diagram that illustrates a computer system 100 whichcan assist in implementing the methods, flows, components, modules,systems, or the apparatus disclosed herein. Computer system 100 includesa bus 102 or other communication mechanism for communicatinginformation, and a processor 104 (or multiple processors 104 and 105)coupled with bus 102 for processing information. Computer system 100also includes a main memory 106, such as a random-access memory (RAM) orother dynamic storage device, coupled to bus 102 for storing informationand instructions to be executed by processor 104. Main memory 106 alsomay be used for storing temporary variables or other intermediateinformation during execution of instructions to be executed by processor104. Computer system 100 further includes a read only memory (ROM) 108or other static storage device coupled to bus 102 for storing staticinformation and instructions for processor 104. A storage device 110,such as a magnetic disk or optical disk, is provided and coupled to bus102 for storing information and instructions.

Computer system 100 may be coupled via bus 102 to a display 112, such asa cathode ray tube (CRT) or flat panel or touch panel display fordisplaying information to a computer user. An input device 114,including alphanumeric and other keys, is coupled to bus 102 forcommunicating information and command selections to processor 104.Another type of user input device is cursor control 116, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to processor 104 and for controllingcursor movement on display 112. This input device typically has twodegrees of freedom in two axes, a first axis (e.g., x) and a second axis(e.g., y), that allows the device to specify positions in a plane. Atouch panel (screen) display may also be used as an input device.

According to one embodiment, portions of a process herein may beperformed by computer system 100 in response to processor 104 executingone or more sequences of one or more instructions contained in mainmemory 106. Such instructions may be read into main memory 106 fromanother computer-readable medium, such as storage device 110. Executionof the sequences of instructions contained in main memory 106 causesprocessor 104 to perform the process steps described herein. One or moreprocessors in a multi-processing arrangement may also be employed toexecute the sequences of instructions contained in main memory 106. Inan alternative embodiment, hard-wired circuitry may be used in place ofor in combination with software instructions. Thus, the descriptionherein is not limited to any specific combination of hardware circuitryand software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 104 forexecution. Such a medium may take many forms, including but not limitedto, non-volatile media, volatile media, and transmission media.Non-volatile media include, for example, optical or magnetic disks, suchas storage device 110. Volatile media include dynamic memory, such asmain memory 106. Transmission media include coaxial cables, copper wireand fiber optics, including the wires that comprise bus 102.Transmission media can also take the form of acoustic or light waves,such as those generated during radio frequency (RF) and infrared (IR)data communications. Common forms of computer-readable media include,for example, a floppy disk, a flexible disk, hard disk, magnetic tape,any other magnetic medium, a CD-ROM, DVD, any other optical medium,punch cards, paper tape, any other physical medium with patterns ofholes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip orcartridge, a carrier wave as described hereinafter, or any other mediumfrom which a computer can read.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to processor 104 forexecution. For example, the instructions may initially be borne on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 100 canreceive the data on the telephone line and use an infrared transmitterto convert the data to an infrared signal. An infrared detector coupledto bus 102 can receive the data carried in the infrared signal and placethe data on bus 102. Bus 102 carries the data to main memory 106, fromwhich processor 104 retrieves and executes the instructions. Theinstructions received by main memory 106 may optionally be stored onstorage device 110 either before or after execution by processor 104.

Computer system 100 may also include a communication interface 118coupled to bus 102. Communication interface 118 provides a two-way datacommunication coupling to a network link 120 that is connected to alocal network 122. For example, communication interface 118 may be anintegrated services digital network (ISDN) card or a modem to provide adata communication connection to a corresponding type of telephone line.As another example, communication interface 118 may be a local areanetwork (LAN) card to provide a data communication connection to acompatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 118 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

Network link 120 typically provides data communication through one ormore networks to other data devices. For example, network link 120 mayprovide a connection through local network 122 to a host computer 124 orto data equipment operated by an Internet Service Provider (ISP) 126.

ISP 126 in turn provides data communication services through theworldwide packet data communication network, now commonly referred to asthe “Internet” 128. Local network 122 and Internet 128 both useelectrical, electromagnetic or optical signals that carry digital datastreams. The signals through the various networks and the signals onnetwork link 120 and through communication interface 118, which carrythe digital data to and from computer system 100, are exemplary forms ofcarrier waves transporting the information.

Computer system 100 can send messages and receive data, includingprogram code, through the network(s), network link 120, andcommunication interface 118. In the Internet example, a server 130 mighttransmit a requested code for an application program through Internet128, ISP 126, local network 122 and communication interface 118. Onesuch downloaded application may provide for a method as describedherein, for example. The received code may be executed by processor 104as it is received, and/or stored in storage device 110, or othernon-volatile storage for later execution. In this manner, computersystem 100 may obtain application code in the form of a carrier wave.

Although specific reference may be made in this text to the use ofembodiments in the context of metrology or inspection apparatus used toinspect or measure items in association with, e.g., optical lithographyand/or manufacture of ICs, it will be appreciated that the methods andapparatus described herein may be used in other applications, forexample imprint lithography, the use or manufacture of integratedoptical systems, the use or manufacture of guidance and detectionpatterns for magnetic domain memories, the use or manufacture offlat-panel displays, the use or manufacture of liquid-crystal displays(LCDs), the use or manufacture of thin film magnetic heads, etc.

The substrate referred to herein may be processed, before or afterexposure/patterning, in for example a track (a tool that typicallyapplies a layer of resist to a substrate and develops thepatterned/exposed resist), a metrology tool and/or an inspection tool.Where applicable, the disclosure herein may be applied to such and othersubstrate processing tools. Further, the substrate may be processed morethan once, for example in order to create a multi-layer IC, so that theterm substrate used herein may also refer to a substrate that alreadycontains multiple processed or unprocessed layers.

Although specific reference may have been made above to the use ofembodiments of the disclosure in the context of optical lithography, itwill be appreciated that the disclosure may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of less than about 400 nm and greater than about 20nm, or about 365, 355, 248, 193, 157 or 126 nm), extreme ultra-violet(EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), aswell as particle beams, such as ion beams or electron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and/or electrostaticoptical components.

While specific embodiments have been described above, it will beappreciated that the disclosure may be practiced otherwise than asdescribed. For example, an embodiment may take the form of a computerprogram containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a non-transitorydata storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein, or a transitorymedium having such a computer program therein. Further, themachine-readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent data storage media.

Relative dimensions of components in drawings may be exaggerated forclarity. Within the description of drawings, the same or like referencenumbers refer to the same or like components or entities, and only thedifferences with respect to the individual embodiments are described. Asused herein, unless specifically stated otherwise, the term “or”encompasses all possible combinations, except where infeasible. Forexample, if it is stated that a component may include A or B, then,unless specifically stated otherwise or infeasible, the component mayinclude A, or B, or A and B. As a second example, if it is stated that acomponent may include A, B, or C, then, unless specifically statedotherwise or infeasible, the component may include A, or B, or C, or Aand B, or A and C, or B and C, or A and B and C.

It will be appreciated that the embodiments of the present disclosureare not limited to the exact construction that has been described aboveand illustrated in the accompanying drawings, and that variousmodifications and changes may be made without departing from the scopethereof. The present disclosure has been described in connection withvarious embodiments, other embodiments of the invention will be apparentto those skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

Embodiments of the present disclosure can be further described by thefollowing clauses.

-   -   1. A non-transitory computer-readable medium having instructions        that, when executed by a computer, cause the computer to execute        a method for aligning a measured image of a pattern printed on a        substrate with a design layout, the method comprising:        -   obtaining a design layout of a pattern to be printed on a            substrate and a measured image of the pattern printed on the            substrate;        -   performing a simulation process to generate simulated            contours of the design layout for a plurality of process            conditions of a patterning process;        -   identifying a set of disfavored locations based on the            simulated contours; and        -   performing an image alignment process to align the measured            image with a selected contour of the simulated contours            using locations other than the set of disfavored locations.    -   2. The computer-readable medium of clause 1 further comprising:        -   determining a parameter associated with the measured image            based on the image alignment process, and        -   adjusting at least one of the design layout, a patterning            device having the design layout, or the patterning process,            based on the parameter.    -   3. The computer-readable medium of clause 1, wherein performing        the simulation process includes:        -   generating each of the simulated contours for a different            process condition.    -   4. The computer-readable medium of clause 3, wherein each of the        process conditions includes one or more of a lens effect of an        apparatus used to print the pattern on the substrate or a resist        effect of a resist on the substrate.    -   5. The computer-readable medium of clause 1, wherein performing        the simulation process includes:        -   obtaining a mask design layout by performing an optimal            proximity correction process on the design layout, and        -   generating the simulated contours based on the design layout            and the mask design layout.    -   6. The computer-readable medium of clause 1, wherein the        selected contour corresponds to a nominal process condition.    -   7. The computer-readable medium of clause 1, wherein identifying        the set of disfavored locations includes:        -   identifying a location on the simulated contours as a            disfavored location based on (a) a deviation between the            location and a corresponding location on a contour of the            measured image exceeding a first threshold, (b) a process            condition variation at the location exceeding a second            threshold, (c) a determination that the simulated contours            are asymmetric at the location, or (d) a determination that            one or more of the simulated contours are broken at the            location.    -   8. The computer-readable medium of clause 1, wherein the method        further comprises:        -   identifying a set of favored locations on the simulated            contours based on (a) a deviation between a location on the            simulated contours and corresponding location on a contour            of the measured image satisfying a third threshold, (b) a            process condition variation at the location satisfying a            fourth threshold, or (c) a determination that the simulated            contours are symmetric the location where, and        -   wherein performing the image alignment process includes:            performing the image alignment process between the measured            image and the selected contour at a plurality of locations            on the simulated contours, wherein the plurality of            locations includes the set of favored locations.    -   9. The computer-readable medium of clause 8, wherein performing        the image alignment process includes:        -   excluding the set of disfavored locations from the plurality            of locations for the image alignment process.    -   10. The computer-readable medium of clause 1 further comprising:        -   performing a measurement to obtain a deviation between the            selected contour and a contour of the measured image at a            set of favored locations, and        -   adjusting the selected contour at the set of favored            locations for reducing the deviation, wherein the adjusting            generates an adjusted selected contour.    -   11. The computer-readable medium of clause 10 further        comprising:        -   performing the image alignment process between the measured            image and the adjusted selected contour at the set of            favored locations.    -   12. The computer-readable medium of clause 10 further        comprising:        -   performing a simulation process to generate a predicted            measured image from the adjusted selected contour, and        -   performing the image alignment process between the measured            image and the predicted measured image at the set of favored            locations.    -   13. The computer-readable medium of clause 1 further comprising:        -   performing a simulation process to generate a predicted            measured image from the selected contour, and        -   performing the image alignment process between the measured            image and the predicted measured image at a set of favored            locations.    -   14. The computer-readable medium of clause 13 further        comprising:        -   adjusting the predicted measured image to reduce a deviation            between a contour of the predicted measured image and a            contour of the measured image at the set of favored            locations, wherein the adjusting generates an adjusted            predicted measured image, and        -   performing the image alignment process between the measured            image and the adjusted predicted measured image at the set            of favored locations.    -   15. The computer-readable medium of clause 1, wherein the        measured image is obtained using an image capture device.    -   16. A non-transitory computer-readable medium having        instructions that, when executed by a computer, cause the        computer to execute a method for aligning a measured image of a        pattern printed on a substrate with a design layout, the method        comprising:        -   obtaining a design layout of a pattern to be printed on a            substrate and a measured image of the pattern printed on the            substrate;        -   performing a simulation process to generate simulated            results of the design layout for a plurality of process            conditions of a patterning process;        -   identifying a set of disfavored locations based on the            simulated results; and        -   performing an image alignment process between the measured            image and the design layout by aligning the measured image            with a selected result of the simulated results using            locations other than the set of disfavored locations.    -   17. The computer-readable medium of clause 16, wherein the        simulated results include simulated contours of the design        layout.    -   18. The computer-readable medium of clause 16, wherein the        selected result is a selected contour of the design layout        corresponding to a nominal process condition.    -   19. The computer-readable medium of clause 16, wherein the        method further includes:        -   performing a simulation process to generate a predicted            measured image from the selected result, and        -   wherein performing the image alignment process includes            aligning the measured image with the predicted measured            image using locations at a set of favored locations, the set            of favored locations excluding the set of disfavored            locations.    -   20. The computer-readable medium of clause 19 further        comprising:        -   adjusting the predicted measured image to reduce a deviation            between a contour of the predicted measured image and a            contour of the measured image at the set of favored            locations, wherein the adjusting generates an adjusted            predicted measured image, and        -   performing the image alignment process between the measured            image and the adjusted predicted measured image at the set            of favored locations.    -   21. A non-transitory computer-readable medium having        instructions that, when executed by a computer, cause the        computer to execute a method for aligning a measured image of a        pattern printed on a substrate with a design layout, the method        comprising:        -   obtaining a design layout of a pattern to be printed on a            substrate and a measured image of the pattern printed on the            substrate;        -   performing a simulation process to generate simulated            contours of the design layout for a plurality of process            conditions of a patterning process;        -   identifying a set of disfavored locations based on the            simulated contours;        -   performing a simulation process to generate a predicted            measured image from a selected contour of the simulated            contours; and        -   performing an image alignment process to align the measured            image with the predicted measured image using locations            other than the set of disfavored locations.    -   22. The computer-readable medium of clause 21 further        comprising:        -   adjusting the selected contour for reducing a deviation            between the selected contour and a contour of the measured            image at a set of favored locations, wherein the adjusting            generates an adjusted predicted measured image.    -   23. The computer-readable medium of clause 22 further        comprising:        -   performing the image alignment process between the measured            image and the adjusted predicted measured image at the set            of favored locations.    -   24. A method for aligning a measured image of a pattern printed        on a substrate with a design layout, the method comprising:        -   obtaining a design layout of a pattern to be printed on a            substrate and a measured image of the pattern printed on the            substrate;        -   performing a simulation process to generate simulated            contours of the design layout for a plurality of process            conditions of a patterning process;        -   identifying a set of disfavored locations based on the            simulated contours; and        -   performing an image alignment process to align the measured            image with a selected contour of the simulated contours            using locations other than the set of disfavored locations.    -   25. The method of clause 24, wherein performing the simulation        process includes: generating each of the simulated contours for        a different process condition.    -   26. The method of clause 25, wherein a process condition of the        process conditions includes one or more of lens effect of an        apparatus used to print the pattern on the substrate or a resist        effect on the substrate.    -   27. The method of clause 24, wherein performing the simulation        process includes:        -   performing an optimal proximity correction process on the            design layout to generate a corrected design layout, and        -   generating the simulated contours of the corrected design            layout.    -   28. The method of clause 24, wherein performing the image        alignment process includes:        -   identifying one of the simulated contours corresponding to a            specified process condition as the selected contour.    -   29. The method of clause 24, wherein identifying the set of        disfavored locations includes:        -   identifying a location on the simulated contours as a            disfavored location based on (a) a deviation between the            location and a corresponding location on a contour of the            measured image exceeding a first threshold, (b) a process            condition variation at the location exceeding a second            threshold, (c) a determination that the simulated contours            are asymmetric at the location, or (d) a determination that            one or more of the simulated contours are broken at the            location.    -   30. The method of clause 24, wherein the method further        includes:        -   identifying a set of favored locations on the simulated            contours based on (a) a deviation between a location on the            simulated contours and corresponding location on a contour            of the measured image satisfying a third threshold, (b) a            process condition variation at the location satisfying a            fourth threshold, or (c) a determination that the simulated            contours are symmetric the location where, and        -   wherein performing the image alignment process includes:            performing the image alignment process between the measured            image and the selected contour at a plurality of locations            on the simulated contours, wherein the plurality of            locations includes the set of favored locations.    -   31. The method of clause 30, wherein performing the image        alignment process includes:        -   excluding the set of disfavored locations from the plurality            of locations for the image alignment process.    -   32. The method of clause 24 further comprising:        -   performing a measurement to obtain a deviation between the            selected contour and a contour of the measured image at a            set of favored locations, and        -   adjusting the selected contour at the set of favored            locations for reducing the deviation, wherein the adjusting            generates an adjusted selected contour.    -   33. The method of clause 32 further comprising:        -   performing the image alignment process between the measured            image and the adjusted selected contour at the set of            favored locations.    -   34. The method of clause 32 further comprising:        -   performing a simulation process to generate a predicted            measured image from the adjusted selected contour, and        -   performing the image alignment process between the measured            image and the predicted measured image at the set of favored            locations.    -   35. The method of clause 24 further comprising:        -   performing a simulation process to generate a predicted            measured image from the selected contour, and        -   performing the image alignment process between the measured            image and the predicted measured image at a set of favored            locations.    -   36. The method of clause 35 further comprising:        -   adjusting the predicted measured image to reduce a deviation            between a contour of the predicted measured image and a            contour of the measured image at the set of favored            locations, wherein the adjusting generates an adjusted            predicted measured image, and        -   performing the image alignment process between the measured            image and the adjusted predicted measured image at the set            of favored locations.    -   37. The method of clause 24, wherein the measured image is        obtained using an image capture device.    -   38. An apparatus comprising:        -   a memory storing a set of instructions; and        -   at least one processor configured to execute the set of            instructions to cause the apparatus to perform a method as            described in any of clauses 24-37.    -   39. An inspection system comprising:        -   An image capturing system;        -   a memory storing a set of instructions; and        -   at least one processor configured to execute the set of            instructions to cause the apparatus to perform a method as            described in any of clauses 24-37.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the disclosure as described without departing from thescope of the claims set out below.

1. A non-transitory computer-readable medium having instructions that,when executed by a computer system, are configured to cause the computersystem to at least: obtain a design layout of a pattern to be printed ona substrate and a measured image of the pattern printed on thesubstrate; perform a simulation process to generate simulated contoursof the design layout for a plurality of process conditions of apatterning process; identify a set of disfavored locations based on thesimulated contours; and perform an image alignment process to align themeasured image with a selected contour of the simulated contours usinglocations other than the set of disfavored locations.
 2. Thecomputer-readable medium of claim 1, wherein the instructions arefurther configured to cause the computer system to: determine aparameter associated with the measured image based on the imagealignment process, and adjust, based on the parameter, at least oneselected from: the design layout, a patterning device having the designlayout, or the patterning process.
 3. The computer-readable medium ofclaim 1, wherein the instructions configured to cause the computersystem to perform the simulation process are further configured to causethe computer system to generate each of the simulated contours for adifferent process condition.
 4. The computer-readable medium of claim 3,wherein each of the process conditions includes a lens effect of anapparatus used to print the pattern on the substrate and/or a resisteffect of a resist on the substrate.
 5. The computer-readable medium ofclaim 1, wherein the instructions configured to cause the computersystem to perform the simulation process are further configured to causethe computer system to: obtain a mask design layout by performing anoptimal proximity correction process on the design layout, and generatethe simulated contours based on the design layout and the mask designlayout.
 6. The computer-readable medium of claim 1, wherein the selectedcontour corresponds to a nominal process condition.
 7. Thecomputer-readable medium of claim 1, wherein the instructions configuredto cause the computer system to identify the set of disfavored locationsare further configured to cause the computer system to identify alocation on the simulated contours as a disfavored location based on (a)a deviation between the location and a corresponding location on acontour of the measured image exceeding a first threshold, (b) a processcondition variation at the location exceeding a second threshold, (c) adetermination that the simulated contours are asymmetric at thelocation, or (d) a determination that one or more of the simulatedcontours are broken at the location.
 8. The computer-readable medium ofclaim 1, wherein the instructions are further configured to cause thecomputer system to: identify a set of favored locations on the simulatedcontours based on (a) a deviation between a location on the simulatedcontours and corresponding location on a contour of the measured imagesatisfying a third threshold, (b) a process condition variation at alocation on a contour satisfying a fourth threshold, or (c) adetermination that the simulated contours are symmetric at a location onthe simulated contours, and wherein the instructions configured to causethe computer system to perform the alignment process are furtherconfigured to cause the computer system to perform the image alignmentprocess between the measured image and the selected contour at aplurality of locations on the simulated contours, wherein the pluralityof locations includes the set of favored locations.
 9. Thecomputer-readable medium of claim 8, wherein the instructions configuredto cause the computer system to perform the alignment process arefurther configured to cause the computer system to exclude the set ofdisfavored locations from the plurality of locations for the imagealignment process.
 10. The computer-readable medium of claim 1, whereinthe instructions are further configured to cause the computer system to:perform a measurement to obtain a deviation between the selected contourand a contour of the measured image at a set of favored locations, andadjust the selected contour at the set of favored locations for reducingthe deviation, wherein the adjustment generates an adjusted selectedcontour.
 11. The computer-readable medium of claim 10, wherein theinstructions are further configured to cause the computer system toperform the image alignment process between the measured image and theadjusted selected contour at the set of favored locations.
 12. Thecomputer-readable medium of claim 10, wherein the instructions arefurther configured to cause the computer system to: perform a simulationprocess to generate a predicted measured image from the adjustedselected contour, and perform the image alignment process between themeasured image and the predicted measured image at the set of favoredlocations.
 13. The computer-readable medium of claim 1, wherein theinstructions are further configured to cause the computer system tofurther comprising: perform a simulation process to generate a predictedmeasured image from the selected contour, and perform the imagealignment process between the measured image and the predicted measuredimage at a set of favored locations.
 14. The computer-readable medium ofclaim 13, wherein the instructions are further configured to cause thecomputer system to: adjust the predicted measured image to reduce adeviation between a contour of the predicted measured image and acontour of the measured image at the set of favored locations, whereinthe adjustment generates an adjusted predicted measured image, andperform the image alignment process between the measured image and theadjusted predicted measured image at the set of favored locations. 15.The computer-readable medium of claim 1, wherein the measured image isobtained using an image capture device.
 16. An apparatus comprising: amemory storing a set of instructions; and at least one processorconfigured to execute the set of instructions to cause the apparatus toat least perform a method of: obtain obtaining a design layout of apattern to be printed on a substrate and a measured image of the patternprinted on the substrate; perform a simulation process to generatesimulated contours of the design layout for a plurality of processconditions of a patterning process; identify a set of disfavoredlocations based on the simulated contours; and perform an imagealignment process to align the measured image with a selected contour ofthe simulated contours using locations other than the set of disfavoredlocations.
 17. A non-transitory computer-readable medium havinginstructions that, when executed by a computer system, cause thecomputer system to at least: obtain a design layout of a pattern to beprinted on a substrate and a measured image of the pattern printed onthe substrate; perform a simulation process to generate simulatedresults of the design layout for a plurality of process conditions of apatterning process; identify a set of disfavored locations based on thesimulated results; and perform an image alignment process between themeasured image and the design layout by aligning the measured image witha selected result of the simulated results using locations other thanthe set of disfavored locations.
 18. The computer-readable medium ofclaim 17, wherein the instructions are further configured to cause thecomputer system to perform a simulation process to generate a predictedmeasured image from the selected result, and wherein the instructionsconfigured to cause the computer system to perform the image alignmentprocess are further configured to cause the computer system to align themeasured image with the predicted measured image using locations at aset of favored locations, the set of favored locations excluding the setof disfavored locations.
 19. The computer-readable medium of claim 18,wherein the instructions are further configured to cause the computersystem to: adjust the predicted measured image to reduce a deviationbetween a contour of the predicted measured image and a contour of themeasured image at the set of favored locations, wherein the adjustmentgenerates an adjusted predicted measured image, and perform the imagealignment process between the measured image and the adjusted predictedmeasured image at the set of favored locations.
 20. Thecomputer-readable medium of claim 17, wherein the instructions arefurther configured to cause the computer system to: determine aparameter associated with the measured image based on the imagealignment process, and adjust, based on the parameter, at least oneselected from: the design layout, a patterning device having the designlayout, or the patterning process.